Ash and friends come across a group of kindergarten students who have befriended a Trubbish after rescuing it from a junkyard. The students want to keep it in their class, but their teacher, Daniela, will have no part of it! She thinks a Trubbish will be impossible to care for, as well as being unsafe for the class.
Ash offers to go and talk to the kids on behalf of their teacher, but when he sees how much fun the kids are having in their clubhouse—and how much they really care about Trubbish—he ends up siding with them! When Daniela still refuses to allow Trubbish to stay, Ash challenges her to a battle. As they’re about to begin, the secret clubhouse that the kids and Trubbish built out of junk starts to collapse!
Ash and Pikachu attempt to help Daniela and her Deerling stop the clubhouse from falling down. As they struggle to hold up the toppling wall of junk, the Trubbish saves the day with a powerful series of Sludge attacks! Seeing how much the kids care about Trubbish and vice versa, the teacher reconsiders her position and asks Trubbish to stay with the class after all. And for his role in helping protect the children, Ash is given a mysterious Pokémon Egg!